In the electronics industry, there is an ever increasing demand for semiconductor parts such as integrated circuit chips, semiconductor devices, transistors, diodes, hybrid circuits, and the like (hereinafter parts), to be produced less expensively and with smaller dimensions. Manufacture of these parts is not perfect electrically or mechanically. Although defects in some families of parts are quite rare, the complexity of the part and the consequence of failure usually dictate that the parts meet a high standard of quality. In other words, every part or, in some cases, at least a sample of the parts must undergo an electrical test and/or a mechanical inspection. Ordinarily, a very large quantity of identical parts are tested and inspected. This testing and inspection step can be a significant bottleneck in electronic part manufacture. One way to increase manufacturing productivity of such electronic parts, and thereby reduce the per unit cost, is to increase the speed and accuracy of the testing and inspection of the parts.
To improve testing efficiency, an automatic part handler delivers and removes the parts from the electrical test equipment. The electrical test of the parts measures certain electrical characteristics to ascertain the quality of the part. The electrical test is accomplished via a testing contactor which engages the leads of the particular part. In some cases, part testing is performed at a temperature other than ambient temperature to further measure certain operating characteristics. To improve efficiency and accuracy, parts are supplied to and removed from the testing contactor(s) by an automatic part handler which often contains a temperature conditioning means.
A significant cost and efficiency consideration for all part handlers is alignment between the part to be tested and the testing contactor. Precise alignment is necessary to insure proper electrical contact. As parts evolve into smaller packages with more leads, alignment between the part and the test contactor must be even more precise. For example, because part lead widths are now on the order of 0.010 inches and lead pitches are on the order of 0.020 inches, even "small" x, y and theta alignment errors will result in an unsuccessful electrical test. Repeatability of these precise alignment requirements is essential because thousands of very nearly identical parts must accurately and electrically engage the testing contactor.
In the part handler field, most of the prior art precisely aligns parts by using changeover kits or part holders. See, for example, U.S. Pat. No. 5,290,134 to Baba and U.S. Pat. No. 5,148,100 to Sekiba. A changeover kit mechanically configures the handler to adjust all part handling mechanisms, thermal storage systems, contactors, and other portions of the handler to run a particular part. The most expensive portion of a changeover kit are part carriers (also called precising pockets). A part carrier, as part of a changeover kit, typically houses at least one part in a machined pocket that has tapered sides so as to receive and precisely locate a part. The part carrier repeatedly orients a part by maintaining very tight tolerances tailored to the dimensions of the type of part to be tested. The part carriers are closely machined, usually from aluminum or engineering plastic, and are easily damaged and must be carefully maintained.
Changeover kits, and more particularly part carriers, have numerous limitations. First, because the carrier recess must be tightly machined to provide precise orientation, parts with out-of-spec dimensions present serious problems. A part that is slightly too large will often become jammed in the carrier. To fix a jam, an operator must attend to the handler and oftentimes the handler must be shut down. A part that is too small will be loose and become misaligned at the contactor interface. Damage to the contactor can result from inserting misaligned parts. Second, every part having different dimensions requires a different changeover kit, which includes corresponding part carriers. Therefore, because there are hundreds of different part types hundreds of changeover kits are required. Production control and maintenance of so many changeover kits becomes a time-consuming and costly endeavor. Third, changeover kits are expensive. On large full-production handlers, each changeover kit can cost between ten and thirty-five thousand dollars.
In addition to the problems in the prior art described above, the mass of the part carriers further hinders the efficiency of the handler. Relative to a part, the part carrier's mass is tremendous. The additional mass of the part carriers slows the various transport mechanisms and can impart damaging forces and vibration into the process during acceleration and deceleration. The part carrier mass also slows thermal conditioning of the parts.
Another shortcoming in the handler prior art is the lack of integrated lead and dimensional inspection. The manufacturing process usually includes a visual inspection of the part, including the part leads and pin #1 orientation. In the prior art, this manufacturing step is often performed separately from the electrical testing step. An additional concern is that parts are occasionally damaged during electrical testing by the handler or testing contactor itself. For efficient part manufacture, it is vital that part leads be inspected before, during and after electrical test handling.
Yet another problem of handlers in the prior art is their large bulk and footprint. Factory floor space can be considerable. Handlers are often removed off the factory floor for maintenance and repair. The smaller the handler, the easier it is to relocate and repair the machine.
It appears that vision-based systems are not employed in the automatic part handling field. However, machine vision methods and apparatus are found in other fields including the circuit board manufacturing prior art. The most common vision-based apparatus in circuit board manufacturing is called "pick and place." The basic pick and place apparatus uses a placement arm, a camera and vision software. The placement arm picks up a part and brings it to a zeroing position where it is observed by the camera. The vision software calculates the x, y and theta corrections necessary to place the part at the desired location. The placement arm makes the corrections dictated by the vision software and places the part accordingly. A somewhat similar apparatus, but used for part testing purposes, is described in U.S. Pat. No. 5,481,202 to Frye. Frye discloses a vision-based system which aligns a part with an electrical testing apparatus exclusively by visual means. By relying exclusively on visual alignment means, however, part testing is slow and cumbersome. More importantly, like the automatic handler prior art described above Frye requires a part carrier to accurately orient the part.
It is therefore a general object of the present invention to improve the efficiency, part alignment, part throughput, and cost-effectiveness of automatic part handlers.
It is a specific object of the present invention to provide a handler which eliminates the need for part carriers.
It is yet another specific object of the present invention to employ machine vision to improve part alignment, part inspection and handler throughput.
It is still another specific object of the present invention to provide parallel paths to increase the handler throughput.